The present invention relates to a drillable casing brush for use in oil and gas wells.
When carrying out work on a well casing it is usual to set a drillable bridge plug or packer in place within the well casing. The bridge plug is lowered into the well on the drill pipe string to the desired depth and mechanically set in place. This may be achieved by rotating the string, to cause the centre of the plug to rotate relative to the outer casing (which is prevented from rotating freely as a result of friction with the inner wall of the well casing) and expend, though other systems are known for setting the plug. Once set the bridge plug seals the well and isolates the depths below it.
The bridge plug may be further secured in place within the well casing by pumping cement into the well to set solid around the bridge plug, both above and below it.
It is necessary to form a fluid tight seal between the well casing and the bridge plug and to this end it is usual to carry out a separate xe2x80x9ccleaning runxe2x80x9d prior to inserting the bridge plug. This entails running a well casing scraper through the well casing to remove dirt and debris adhering to the walls thereof. The cleaning run can add several hours to the well plugging operation and this represents lost rig operating time which can cost thousands of pounds.
It is an object of the present invention to provide a casing brush which can be used in conjunction with a bridge plug, thereby avoiding the need for a separate cleaning run to be carried out on the well casing.
It is a further object of the present invention to provide a method of plugging a well casing in which the cleaning run and plugging operations are combined.
According to a first aspect of the present invention there is provided a casing brush for cleaning the walls of a well casing, the casing brush comprising a body in which are mounted cleaning bristles and an adapter to connect the upper end of the body to the lower end of a bridge plug, wherein the body and the adapter are comprised of a material which is at least drillable by a rock bit.
In use the casing brush is connected beneath the bridge plug using the adapter. Then, both the casing brush and the bridge plug are inserted into the well casing. The casing brush running below the bridge plug cleans the walls of the well casing and thus ensures a clean surface against which to set the bridge plug in place. This is important if an effective seal is to be provided. Since both the well cleaning and well plugging operations are carried out together the downtime of the well is significantly reduced.
Once the well has been serviced the bridge plug, the adapter and the casing brush can be drilled out together using a rock bit, a PDC bit or the like. Generally speaking, a rock bit is the least suitable type of bit employed in drilling well bores which can be used for drilling out the casing brush. Therefore, if the material from which the casing brush is comprised is capable of being drilled by a rock bit it will also be capable of being drilled by any other bit which might be used.
In a preferred embodiment of the present invention the drillable bridge plug is connected to the drillable casing brush via a swivel to facilitate unimpeded rotation of the bridge plug relative to the casing brush. In this regard, it will be understood that rotation of the drill pipe string is necessary to set the plug in place.
Preferably, the swivel may be adapted to provide a fixed (i.e. non-rotational linkage) between the bridge plug and casing brush if the bridge plug is of a type which does not need to be rotated to mechanically set it in place. To this end, the swivel can be locked to prevent rotation of the casing brush relative to the bridge plug. Conveniently, this is achieved by aligning one or more holes in the body of the casing brush with holes in the swivel, and inserting a locking pin through each pair of aligned holes.
Preferably, the casing brush body is comprised of aluminium, but any material which is capable of being drilled by a rock bit will serve the purpose. Alloys or cast iron may also be used.
Preferably, the casing brush body is tubular with the lower end thereof closed and has holes in the side thereof through which cleaning fluid can be pumped to assist the cleaning action of the bristles.
Preferably, slots are provided in and around the adapter at the upper end of the brush body and in and around the lower end of the brush body through which cement can pass to hold the brush fast. This is helpful when the brush comes to be drilled out.
According to a second aspect of the present invention there is provided a bridge plug and a casing brush in combination, the casing brush being connected to the lower end of the bridge plug by means of an adapter, and the bridge plug, the casing brush and the adapter being comprised of a material which is at least drillable by a rock bit.
According to a third aspect of the present invention there is provided a method of cleaning and plugging a well casing in which:
a) a combined bridge plug and casing brush with the casing brush situated below the bridge plug are run down a well casing;
b) the walls of the well casing are cleaned by the casing brush;
c) the bridge plug is set in place; and
d) after the well has been serviced both the bridge plug and the casing brush are drilled out.
Cement may be pumped through holes in the side of the casing brush to set same in place within the well casing. This serves to hold the casing brush fast which assists when it is drilled out.